[PATCH] mfd: macsmc: Fix key count endianness annotation

[PATCH] mfd: macsmc: Fix key count endianness annotation

[Sven Peter]

SMC firmware returns the value of the #KEY key in big-endian unlike most
other keys. Reading it through apple_smc_read_u32() into a plain u32
and then converting with be32_to_cpu() makes sparse complain:

  drivers/mfd/macsmc.c:462:26: sparse: cast to restricted __be32

Read the raw value into a __be32 using apple_smc_read() instead.

Fixes: e038d985c982 ("mfd: Add Apple Silicon System Management Controller")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@intel.com/
Signed-off-by: Sven Peter <sven@kernel.org>
---
 drivers/mfd/macsmc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/mfd/macsmc.c b/drivers/mfd/macsmc.c
index 358feec2d088..514cba7dc897 100644
--- a/drivers/mfd/macsmc.c
+++ b/drivers/mfd/macsmc.c
@@ -410,7 +410,7 @@ static int apple_smc_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct apple_smc *smc;
-	u32 count;
+	__be32 count;
 	int ret;
 
 	smc = devm_kzalloc(dev, sizeof(*smc), GFP_KERNEL);
@@ -461,8 +461,10 @@ static int apple_smc_probe(struct platform_device *pdev)
 	dev_set_drvdata(&pdev->dev, smc);
 	BLOCKING_INIT_NOTIFIER_HEAD(&smc->event_handlers);
 
-	ret = apple_smc_read_u32(smc, SMC_KEY(#KEY), &count);
-	if (ret)
+	ret = apple_smc_read(smc, SMC_KEY(#KEY), &count, sizeof(count));
+	if (ret >= 0 && ret != sizeof(count))
+		ret = -EINVAL;
+	if (ret < 0)
 		return dev_err_probe(smc->dev, ret, "Failed to get key count");
 	smc->key_count = be32_to_cpu(count);
 

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260719-b4-macsmc-be32-fix-637e8bb1692a

Best regards,
--  
Sven Peter <sven@kernel.org>

Re: [PATCH] mfd: macsmc: Fix key count endianness annotation

[Joshua Peisach]

On Sun Jul 19, 2026 at 9:00 AM EDT, Sven Peter wrote:
> SMC firmware returns the value of the #KEY key in big-endian unlike most
> other keys. Reading it through apple_smc_read_u32() into a plain u32
> and then converting with be32_to_cpu() makes sparse complain:
>
>   drivers/mfd/macsmc.c:462:26: sparse: cast to restricted __be32
>
> Read the raw value into a __be32 using apple_smc_read() instead.
>
> Fixes: e038d985c982 ("mfd: Add Apple Silicon System Management Controller")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@intel.com/
> Signed-off-by: Sven Peter <sven@kernel.org>
> ---
>  drivers/mfd/macsmc.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mfd/macsmc.c b/drivers/mfd/macsmc.c
> index 358feec2d088..514cba7dc897 100644
> --- a/drivers/mfd/macsmc.c
> +++ b/drivers/mfd/macsmc.c
> @@ -410,7 +410,7 @@ static int apple_smc_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
>  	struct apple_smc *smc;
> -	u32 count;
> +	__be32 count;
>  	int ret;
>  
>  	smc = devm_kzalloc(dev, sizeof(*smc), GFP_KERNEL);
> @@ -461,8 +461,10 @@ static int apple_smc_probe(struct platform_device *pdev)
>  	dev_set_drvdata(&pdev->dev, smc);
>  	BLOCKING_INIT_NOTIFIER_HEAD(&smc->event_handlers);
>  
> -	ret = apple_smc_read_u32(smc, SMC_KEY(#KEY), &count);
> -	if (ret)
> +	ret = apple_smc_read(smc, SMC_KEY(#KEY), &count, sizeof(count));
> +	if (ret >= 0 && ret != sizeof(count))
> +		ret = -EINVAL;
> +	if (ret < 0)
>  		return dev_err_probe(smc->dev, ret, "Failed to get key count");
>  	smc->key_count = be32_to_cpu(count);

This makes sense, it just feels weird reading because u32 is.. not a
be32 (that gets passed into be32_to_cpu).

I guess it doesn't really matter.

-Josh

Re: [PATCH] mfd: macsmc: Fix key count endianness annotation

[Sven Peter]

On 7/19/26 17:02, Joshua Peisach wrote:
> On Sun Jul 19, 2026 at 9:00 AM EDT, Sven Peter wrote:
>> SMC firmware returns the value of the #KEY key in big-endian unlike most
>> other keys. Reading it through apple_smc_read_u32() into a plain u32
>> and then converting with be32_to_cpu() makes sparse complain:
>>
>>   drivers/mfd/macsmc.c:462:26: sparse: cast to restricted __be32
>>
>> Read the raw value into a __be32 using apple_smc_read() instead.
>>
>> Fixes: e038d985c982 ("mfd: Add Apple Silicon System Management 
>> Controller")
>> Reported-by: kernel test robot <lkp@intel.com>
>> Closes: 
>> https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@intel.com/
>> Signed-off-by: Sven Peter <sven@kernel.org>
>> ---
>>  drivers/mfd/macsmc.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/mfd/macsmc.c b/drivers/mfd/macsmc.c
>> index 358feec2d088..514cba7dc897 100644
>> --- a/drivers/mfd/macsmc.c
>> +++ b/drivers/mfd/macsmc.c
>> @@ -410,7 +410,7 @@ static int apple_smc_probe(struct platform_device 
>> *pdev)
>>  {
>>      struct device *dev = &pdev->dev;
>>      struct apple_smc *smc;
>> -    u32 count;
>> +    __be32 count;
>>      int ret;
>>
>>      smc = devm_kzalloc(dev, sizeof(*smc), GFP_KERNEL);
>> @@ -461,8 +461,10 @@ static int apple_smc_probe(struct 
>> platform_device *pdev)
>>      dev_set_drvdata(&pdev->dev, smc);
>>      BLOCKING_INIT_NOTIFIER_HEAD(&smc->event_handlers);
>>
>> -    ret = apple_smc_read_u32(smc, SMC_KEY(#KEY), &count);
>> -    if (ret)
>> +    ret = apple_smc_read(smc, SMC_KEY(#KEY), &count, sizeof(count));
>> +    if (ret >= 0 && ret != sizeof(count))
>> +        ret = -EINVAL;
>> +    if (ret < 0)
>>          return dev_err_probe(smc->dev, ret, "Failed to get key count");
>>      smc->key_count = be32_to_cpu(count);
>
> This makes sense, it just feels weird reading because u32 is.. not a
> be32 (that gets passed into be32_to_cpu).

count is __be32 now (the SMC firmware returns that value as big-endian 
because Apple likes to think different) and we read that using 
apple_smc_read now which just reads raw bytes. be32_to_cpu then converts 
that to a u32, i.e. the type of smc->key_count. There's no functional 
change here. What's weird about that?


Sven

Re: [PATCH] mfd: macsmc: Fix key count endianness annotation

[Joshua Peisach]

On Sun Jul 19, 2026 at 11:15 AM EDT, Sven Peter wrote:
>
>
> On 7/19/26 17:02, Joshua Peisach wrote:
>> On Sun Jul 19, 2026 at 9:00 AM EDT, Sven Peter wrote:
>>> SMC firmware returns the value of the #KEY key in big-endian unlike most
>>> other keys. Reading it through apple_smc_read_u32() into a plain u32
>>> and then converting with be32_to_cpu() makes sparse complain:
>>>
>>>   drivers/mfd/macsmc.c:462:26: sparse: cast to restricted __be32
>>>
>>> Read the raw value into a __be32 using apple_smc_read() instead.
>>>
>>> Fixes: e038d985c982 ("mfd: Add Apple Silicon System Management 
>>> Controller")
>>> Reported-by: kernel test robot <lkp@intel.com>
>>> Closes: 
>>> https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@intel.com/
>>> Signed-off-by: Sven Peter <sven@kernel.org>
>>> ---
>>>  drivers/mfd/macsmc.c | 8 +++++---
>>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/mfd/macsmc.c b/drivers/mfd/macsmc.c
>>> index 358feec2d088..514cba7dc897 100644
>>> --- a/drivers/mfd/macsmc.c
>>> +++ b/drivers/mfd/macsmc.c
>>> @@ -410,7 +410,7 @@ static int apple_smc_probe(struct platform_device 
>>> *pdev)
>>>  {
>>>      struct device *dev = &pdev->dev;
>>>      struct apple_smc *smc;
>>> -    u32 count;
>>> +    __be32 count;
>>>      int ret;
>>>
>>>      smc = devm_kzalloc(dev, sizeof(*smc), GFP_KERNEL);
>>> @@ -461,8 +461,10 @@ static int apple_smc_probe(struct 
>>> platform_device *pdev)
>>>      dev_set_drvdata(&pdev->dev, smc);
>>>      BLOCKING_INIT_NOTIFIER_HEAD(&smc->event_handlers);
>>>
>>> -    ret = apple_smc_read_u32(smc, SMC_KEY(#KEY), &count);
>>> -    if (ret)
>>> +    ret = apple_smc_read(smc, SMC_KEY(#KEY), &count, sizeof(count));
>>> +    if (ret >= 0 && ret != sizeof(count))
>>> +        ret = -EINVAL;
>>> +    if (ret < 0)
>>>          return dev_err_probe(smc->dev, ret, "Failed to get key count");
>>>      smc->key_count = be32_to_cpu(count);
>>
>> This makes sense, it just feels weird reading because u32 is.. not a
>> be32 (that gets passed into be32_to_cpu).
>
> count is __be32 now (the SMC firmware returns that value as big-endian 
> because Apple likes to think different) and we read that using 
> apple_smc_read now which just reads raw bytes. be32_to_cpu then converts 
> that to a u32, i.e. the type of smc->key_count. There's no functional 
> change here. What's weird about that?
>
>
> Sven

Pfft, brain fart. I thought you were going other way around.

Reviewed-by: Joshua Peisach <jpeisach@ubuntu.com>